This invention relates to a porous inorganic material having pore walls of crystalline titanium oxide and to a method of producing same.
While crystalline titanium oxide has been hitherto used as a white pigment, much attention has been paid in recent years thereon because of the function thereof as a photocatalyst, in particular as a hydrolysis catalyst, a wet solar cell or a catalyst for decomposing pollutants.
Pores of known crystalline titanium oxide are formed between primary particles thereof, but are not present within the primary particle itself. As a consequence, the pores are not uniform and the catalytic efficiency is not high. Thus, when the known crystalline titanium oxide catalyst is used for decomposing NOx, for example, it is necessary to support the catalyst on a porous carrier, to form into a membrane using a binder or to mix same with another porous material in order to increase a contact area with the reactants or to improve the adsorbing characteristics thereof.
The present invention provides an inorganic material having a multiplicity of pores which have a uniform pore diameter and which are defined by pore walls containing crystalline titanium oxide such as anatase or rutile.
The inorganic material can exhibit excellent shape selectivity and efficiently trap molecules or ions in the pores and, hence, is useful for many applications such as an oxidation catalyst and a photocatalyst.
The present invention also provides a method for preparing an inorganic porous material, wherein an organic inorganic mesostructured material containing titanium and having a hexagonal crystal phase is subjected to a heat treatment at a temperature and for a period of time sufficient to form a multiplicity of pores which have a uniform pore diameter and which are defined by pore walls containing crystalline titanium oxide.
In the present specification, the term xe2x80x9cuniform pore diameterxe2x80x9d is intended to refer to such a pore characteristic that a well defined peak is present in a pore distribution pattern obtained according to the MP method (Mikhail, R. S. H.; Brunauer, S.; Bodor, E. E., J. Colloid Interface Sci. Vol. 26, 45-53, 1968) or the BJH method (Barrett, E. P.; Joyner, L. G.; Halenda, P. P., J. Am. Chem. Soc., Vol. 73, 373-380, 1951) which is used in association with a nitrogen absorption isotherm. The term xe2x80x9cpore diameterxe2x80x9d used in the present specification is intended to refer to the diameter at which the peak is present in the above pore distribution pattern.
In the present specification, the term xe2x80x9corganic inorganic mesostructured material containing titanium and having a hexagonal crystal phasexe2x80x9d is intended to refer to a precursor material showing an X-ray diffraction pattern which is obtained using Cu as a target and in which at least two peaks are present in 2xcex8 (CuKxcex1) of 10xc2x0 or less.
It is an object of the present invention to provide a porous inorganic material having a multiplicity of pores defined by crystalline titanium oxide.
Another object of the present invention is to provide a porous inorganic material of the above-mentioned type which has uniform pore diameter and which is useful for various applications.
It is yet a further object of the present invention to provide a method which can produce the above inorganic material.